Method of forming large hollow castings



Dec. 24, 1935.

A. w. BREARLEY 2,025,336

METHOD OF FORMING LARGE HOLLOW CASTINGS Filed March 25, 1934 2Sheet-Sheet l dmrn y Dec. 24, 1935. A. w. BREARLEY 2,025,336

METHOD OF FORMING LARGE HOLLOW CASTINGS Filed March 25, 1954 2Sheets-Sheet 2 Saw Patented Dec. 24, 1935 UNITED STATES PATENT OFFICEMETHOD OF FORMING LARGE HOLLOW oas'rmcs Arthur William Brearley,Sheffield, England Application March 23, 1934, Serial No. 717,067 InGreat Britain March 24, 1933 3 Claims. (01. 22-200) 10 size, to cast theingot solid and to remove thecentral unwanted portion by a machiningoperation.

fI'his process is unduly expensiveand diflicult because the weight oimetal required to be cast is greatly in excess of that which would berequired 15 ii'the ingot were cast hollow, the ingot requires muchgreater time before removal from the mould and for annealing than ifcast hollow and the machining operation is difiicult, laborious andexpensive. Moreover in some cases of very large 2 ingots the extraweight involved by the unwanted central portion brings the total weightof the in-,

got above the load capacity 01' available lifting gear.

One of the main difiiculties to be overcome in the casting of largehollow ingots is the shrinkage oi. the casting after, it has been pouredand has partly.- or wholly-irozen".- Such shrinkage is resisted by thecore and undesirable internal strains, or, in some cases, actual cracksare formed 30 in the inset.

' A further difilculty arises in the casting of heavy hollow ingotsowing to the tendency or the molten metal in very large bulk to erode acore of rammed sand or fire clay'and the liberation from such 5 cores,under. the intense heat, of gases such as water-vapour.

The present invention has torits object the provision of an improvedprocess of casting heavy hollowingots, whether open at both ends oronlyat one end.

Another object is the casting of such heavy hollowingots ln'such amanner that they are free from internal strains or cracks after theyhave cooled. r

A Anothenobject is the utilization of loose dry sand, as to rammed ormoist coherent sand,v in, the casting of heavy hollow ingots.

Another object is'the provision of' a process of 50 casting heavy hollowingots in which the core maintains its form rigidly so long as isrequired for the poured steel ingot to freeze sufliciently to becomeseli' maintaining as to its shape and the molten steel, when poured,does not come into 55 direct contact with the core which may evolvegases and may be eroded or disintegrated by the molten metal. I

Other objects and advantages of the invention will be appreciated fromthe following description and accompanying drawings. 5

It has heretofore been proposed, for the purpose of preventingblistering of the interior surface of a hollow ingot to cast it about acollapsible core comprising a thin nickel plated tube filled with loosesand or other refractory material. According 'to this proposal the thinnickel plated core tube became fused to the molten metal and, uponcontraction, the loose packing of sand was crushed. .According toanother prior proposal intended for the production of relatively lighthollow castings, such as ordnance and projectiles therefore the corecomprised sand rammed within a shell of sheet iron which melted andformed part of.the casting. In this latter process the sheet iron wasfor ,the purpose of providing a cleaner mould than would be provided bysand alone thusto prevent the formation of blow holes and irregularitiesin the casting. It has also been proposed to provide a ieeder headcomprising an inner liner of thin sheet metal surrounded by looselypacked sand or other insulating material andto embed a closed case 01'sheet iron containing a. non-metallic or silicious body wholly within aningot or other casting. Light tubular, articles such as iron pipes havebeen cast in a sand mould on to an internal shell of thinsheet steel orwrought iron filled with sand. All these proposals relate tocomparatively light castings and not to heavy ingots of the nature ofthose with which the present invention is concerned. It has not hitherto.been practical to utilize sand v for heavy castings where thehydrostatic pressure of the large bulk of molten metal may exceed thestiffness of the sand.

According to the present invention in a process 40 of casting heavyhollow steel ingots about a core comprising a thin walled hollowprotector of metal, capable of blending or alloying with the steel,filled with loose dry sand, the sand sinters at or near the meltingpoint oithe steel, the hollow protector is only sufilciently thick tosupport the sand without melting until after at least the surface layersof the sand have been sintered by the intense heat 01' the molten steel,the steel is flowed into the mould at-the bottom and fills the mould'from the bottom upwards substantially without turbulence and the sand is.broken and loosened after the steel has frozen sufilciently to form inproximity to the core a solid wall of sufficient strengthto maintain theshape of the hollow ingot, thus permitting unimpeded contraction of theingot as it cools further.

The functions'of the thin metal protector and of the sand arecomplementary to each other. The thin metal protector first supports andmaintains the desired shape of the loose dry sand core, secondly itprotects the loose sand core from being disintegrated by the moltensteel and thirdly it permits the sand to be sintered without deformationof the core. The sand on the other hand, 'by the pressure exerted by iton the surface of the protector owing to its loose or mobile formprevents the collapse of the protector under the very great hydrostaticpressure of the molten steel. The sand moreover sinters before theprotector melts, as it may in some cases, and thus forms a coherent wallof sufiicient strength to withstand the hydrostatic pressure of thestill molten 'metal against it. It is of secondary importance whether ornot the protector melts after the sintering of the sand because when thesand is sintered, the function of the protector is no longer necessary.

As above stated as soon as the cast steel has solidified sufiiciently toretain the shape of the ingot the sintered sand is broken and loosened,the contraction of the ingot thus being permitted to take place withlittle or no restraint as the ingot cools.

The flowing of the molten steel into, the bottom of the mould andfilling of the mould from the bottom upwards substantially withoutturbulenceis of importance, since pouring the steel into the top of themould would inevitably set up turbulence and splashing which might causepremature melting of the protector before the sand has sinteredsufficiently to maintain its shape.

.In carrying out the invention a fracturing device is preferablyembedded in the sand and, after the steel has frozen sufiiciently,'it ismoved and preferably withdrawn to cause the sand to crumble. In castinga hollow ingot the steel may be poured through a central geat or conduitin known manner so that the molten steel is introduced through thecenter of the core to the bottom of the mould. In this case the geatissurrounded by a thin protector with an annular space between the geatand the protector filled'with loose dry sand and, after the steel hasfrozen sumciently, the sand is fractured and loosened by movement of thegeat.

In casting a hollow ingot closed at one end the protector may be a sheetmetal vessel having .a closed and an open end. It is filled with loosedry sand and supported in the mould with its closed end lowermost andabove the base of the mould and with its open end above the top of theingot to be cast. a

Other objects are to apply the invention to the casting ofslab ingotsandcomposite ingots.

In the accompanying drawings:-- Figure 1 is a sectional elevation of aningot mould and core according to the present invention. I

Figure 2 is a plan of Figure 1.

/ .Figure 3 is a view similar to Figure 1 illustrating a modification.

and a geat or conduit I2,for the molten metal is arranged at about thecentre of the mould and is connected. with runner bricksv l3 fitted inthe plate ll.

The geat illustrated is of the type in which dry granular packing I4 ispoured into the annular 5 space between an outer metal case i 5 and aninher refractory liner tube l6. I

A protector in the form of a hollow cylinder ll of sheet metal issupported on the casting plate ll co-axial with the geat or conduit I2and the 10 annular space between the protector I1 and the outer metalcase l5 of the conduit is filled with dry sand l8 which is in a drycondition and may tector II.

It is advisable to feed the ingot through a number of equally spacedrunner bricks l3, four of the feed apertures I! from such bricks beingshown in Figure 2, so that the steel may be delivered at an equalizedtemperature in different parts of the ingot, thereby preventing theproduction of a relatively hot and cold side which may lead to crackingwhen the ingot freezes.

At a suitable interval after casting, depending on the mass of theingot, the central conduit or geat I5 is drawn out, allowing the sand l8to collapse. A flange or laterally projecting feet or the like 20 may beprovided onthe outer metal case of the conduit to enable it to standfirmly on the casting plate II and to operate to fracture the sinteredsand l8 when the conduit is extracted.

The'shape of the protector I1 may vary accord- 40 ing to circumstancesand its thickness is governed by the mass and temperature of fluid metalin contact with it, its own melting point and the temperature at whichthe sand it! sinters.

In a specific example an ingot weighing from seven to twenty tons maythus be cast around a protector l1 made from mild steel sheet onesixteenth of an inch thick. In another example an ingot weighing threeto five tons may be cast around a protector I1 made from mild steelsheet of twenty six gauge thick. In bothcases the outer orexposedsurface of the protector remains solid, its inner surface'being'weldedto the casting.

Whether the protector l1 melts wholly or partially during the pouringoperation, it may be arranged to distribute the pressure of the fluidmetal to the main body of the .sand ll (thus preventing the latter fromcrumbling) until it has frit or sintered and is in a condition towithstand that pressure without the aid of the protector.

In the modification illustrated in Figure 3 the geat or conduit 24 isdisposed outside the mould 22 and a rod 2| is embedded in the sand 28inside the protector 21. The rod 2| forms a fracturing or removingdevice so that on withdrawing it, after casting, the sand 28 willcollapse and will oppose no resistance to contraction of the ingot as itfreezes. The geat or conduit 24 may feed more than one mould, two-beingshown in, Figure 3. The molten steel is fed to the base of the mouldthrough runner bricks 25 provided with feed apertures 29as illustratedin Figure 3, arranged in the annular space between the protector 21 andthe mould 22. f

Ifdesired the rod 2| may be provided with 75.

lateral projections to ensure that the sand shall plete core comprisingthe protector ll, 34, supporting the wall of sand 32 and containing therod 33 is supported or suspended in an ingot mould 35, with its closedend 34 the'desired distance from the base of the mould and its openend'above the casting level or top of the ingots The inventionmay alsobe applied to the cor ing of castings other than ingots, especiallywhere it is desirable that the core shall oppose no resistance tocontraction of the casting.

The metal wall of the tube or protector must not be of such thicknessthat it may by itself,

when heated to the temperature of the molten metal in contact therewith,withstand the hydrostatic pressure of the metal, but on the other handmust require interior support at such temperatures in order to maintainits shape. On the other hand the metal wall of the tube must not be sothin that it will melt and permit penetration of molten metal to thesand core prior to the time when the layer of sand next adjacent I thesame has been raised to a sintering temperature. By

the term thin used in the appended claims in describing the thickness ofthe wall of the tube is meant a tube having a wall the thickness ofwhich lies between the limits above set forth. The actual thickness ofthe metal wall of the tube to be used in any particular instance mayvary facing sheet of metal capable of blending or alloying withthe metalto be cast, said sheet being relativelythin so as to readily transmitheat from a body of molten metal to the sand, while at the same timepreventing access of the molten metal thereto until the sand layer nextadjacent the sheet has sintered and become self-sustaining against theaction of molten metal and, after the molten metal has cooledsufficiently to become self-sustaining, destroying the core. g

2. The method of forming an axial cylindrical void or cavity in a largethick walled casting, during a casting operation, with the aid 'of aporeof loose dry sand having the capacity to sinter under heat, whichcomprises the steps of protecting the loose dry sand core by arelatively thin cylindrical facing sheet of metal capable of blending oralloying with the metal to be cast, said sheet readily transmitting heatfrom a body of. molten metal to the sand, while at the same timepreventing access of the molten metal thereto until the sand layer nextadjacent the facing sheet has sintered and forms a rigid wallself-sustaining against the action and pressure of the surrounding bodyof molten metal and-after the molten metal has itself cooledsuillciently to become self-sustaining, destroying the core, includingthe sintered outer wall, to permit free contraction of the casting.

. 3. The method of forming an axial void or cavity in a large thickwalled casting, during a casting operation, with the aid of a core ofloose dry sand having the capacity to sinter under' heat, whichcomprises the steps of protecting the loose dry sand core by arelatively thin facing sheet ,of metal capable of blending or alloyingwith the metal to be cast, said sheet readily transmitting heat from abody of molten metal to the sand, while at the sametime preventingaccess of the molten metal theretountil the sand-layer next adjacent thefacing sheet has sintered and forms a rigid wall self-sustaining-againstthe ac- 40 L the,casting.

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